In the past, vehicles for the purpose of transporting sand, gravel, paving materials and other loose materials which are relatively heavy have often been required to be specialized, either for the type of materials which must be carried or for the particular conditions under which the vehicles must operate. Many vehicles are primarily used in general construction for conveying, moving or delivering large quantities of sand, concrete, rocks, earth or paving materials. Often, large quantities of materials must be transported long distances over existing roadways. Depending upon the particular application, the transported materials may need to be dumped from the belly of the vehicle. Sometimes, vehicles may be required which allow the materials to be dumped from the end of the vehicle. In the past, vehicles which dumped from the belly typically required one specific type of construction. Other vehicles which dumped from the end, as by raising the front end of a truck bed and letting the contents slide through a tailgate, required a different type of construction.
Some types of work or construction may have enough use for a particular specialized dumping activity to justify constructing a particular type of vehicle for the intended purpose, whether belly dumping or end dumping. Other jobs may require more than one specialized dumping capability. Often, there is a need to have one or only a few transport and dumping vehicles which might be useful for multiple purposes. Most available trailers and vehicles are only for one particular purpose, as, for example, the end-dumping trailers shown in U.S. Pat. Nos. 2,718,429; 2,983,548; and 3,232,666. Most of such end-dumping vehicles are entirely without belly-dumping capabilities. Belly-dumping vehicles have also been known; however, such vehicles typically are highly specialized for the particular belly-dumping operation intended, without end-dumping capabilities.
An early attempt to overcome the drawbacks of separate vehicles for specialized purposes included a combination belly-dump/end-dump vehicle for hauling materials, which was disclosed in U.S. Pat. No. 4,289,353. This disclosure showed a vehicle which was intended to be capable of either end dumping or belly dumping. The disclosure showed a vehicle, which included a frame mounted upon wheels and which provided a first pivot support and a second pivot support, with the first pivot support at least level with or lower than the second pivot support. A hopper for containing the materials to be transported and dumped was carried by the frame. The hopper was described as having a gate means located at the bottom for belly dumping. In its lowered or transport position, an arm from the rear of the hopper engaged the first pivot support. A telescopic ram was provided between the front of the frame and the front of the hopper for raising the front end of the hopper and for lifting the hopper rotatably about the first pivot support. After pivoting to a particular angle and before dumping was initiated, a top edge of the hopper became pivotably engaged with the second pivot support. The first and second pivots were alternately engaged upon hydraulically raising the front end of the hopper so that the materials dumped out of the rear of the hopper over the rear of the frame, preferably only after the second pivot engagement occurred. The vehicle disclosed provided the first pivot support ahead of the rear wheels. The second pivot support was shown positioned behind the rear wheels of the vehicle to permit dumping the contents behind the vehicle, not on the frame or rear wheels. Thus, unless the trailer vehicle was securely attached downward in the front, a heavy load in a fully tilted hopper acted downward on a "lever" extending behind the rear axle and that tended to lift the front end of the trailer. Also, the telescopic hydraulic cylinder was attached ahead of the hopper, apparently for maximum leverage when pivoting the hopper. This construction required an extremely long hydraulic cylinder stroke to fully pivot the hopper. A hydraulic cylinder with a large number of telescoping hydraulic stages would be required for a vehicle with this design. Also, the frame for the vehicle, as disclosed, was of a construction requiring multiple side beams extending from the front to the rear of the vehicle along the sides of the hopper to be supported. Upper and lower parallel side beams were provided on each side of the hopper, apparently to provide adequate strength and stability for a fully loaded hopper.
Further, the alternatingly engageable pivot support connections were depicted as including round bar stock pivot bars attached to the hopper and semicircular sockets secured, upwardly directed, on the vehicle for pivotably receiving the pivot bars of the hopper. These upwardly directed sockets did not hold the hopper downward in place when transporting. The weight of the hopper and payload and the hydraulic cylinder attachment were relied upon for holding the hopper down into the frame during transport. Further, when the hopper pivot bars were not engaged in the upwardly opened pivot sockets, the sockets could accumulate rocks, gravel or other materials, as, for example, from loading or unloading the payload. Thus, the lower pivot supports or sockets could accumulate debris when the hopper was pivoted rearward and engaged in the upper pivot sockets for end dumping. The upper sockets could accumulate debris when the hopper is in its lowered/non-pivoted position. When the pivot bars engaged and rotated in the sockets, unnecessary wear and abrasion resulted.
Prior trailers, having belly-dumping capability, were typically provided with bay doors, which typically had to be continuously maintained in a closed position with externally applied force, as with a pneumatic cylinder. The doors were typically actuated to either a fully closed position for filling and transport or to a fully open position for dumping the load of material. The weight of the load in such prior hopper designs continuously acted to push the doors to an open position.
In some alternative of hopper doors, such as those depicted in U.S. Pat. No. 4,289,353, a "clamshell gate" was described as being operated, either hydraulically or pneumatically. The means of operation was not fully described in the '353 patent, as it was said that the operation thereof was known in the art. However, as depicted in the drawings of the '353 patent, the clamshell gates had a substantially continuous arcuate shape, with the lowest part of the arc along the center line of the hopper. Large actuating cylinders were provided to pivot the clamshells either fully closed or fully open. The actuating cylinders were typically air-operated cylinders, which were convenient for purposes of the use of tractor/trailer rigs of the type commonly fitted with air brakes and a corresponding air pressure-generating system. Such pneumatic cylinders did not lend themselves to partial opening, but rather were either fully actuated to an open position or fully actuated to a closed position. Unless a mechanical latch was also used to maintain the clamshell gate into a closed position, the air-operated cylinders would need to maintain a seal so that either pressure or vacuum, depending on the configuration, kept the doors in a closed position until such time as the doors were to be opened, when the cylinders would be actuated so that the gates or the doors would be moved outward to a fully open position. Thus, in these devices, it appears that the forces of granular material against the clamshell doors continuously tended to open the doors.
The opening of the doors with "on" or "off" pneumatic type actuators was sufficiently quick so that one need not be concerned with which of the doors opened first or fastest. Both of the doors, if operating properly, moved swiftly to the fully open position to allow for complete dumping.
Most earlier trailers, of all types, which have had multiple rear wheel assemblies, have had a plurality of vertically extending support struts, typically interposed between each axle, or each set of wheels. The support struts were constructed of a rigid material, supported from a horizontal frame member, above. These support struts were typically made in pairs, one on either side of the trailer. At the lower end of each support strut was a fastening means at which a spring, such as a leaf spring, was connected and suspended between a support strut ahead of an axle and a support strut behind an axle. In the case of two rear axles, typically three pairs of left and right support struts were used: one front pair, one middle pair and one rear pair. The leaf springs were suspended from the middle struts toward the front strut and from the middle strut toward the rear strut. Attached to each of the leaf springs was an axle, and a shock absorber mechanism was also appropriately affixed. Because of the large diameter of the tires, the support struts were required to extend a substantial distance from the upper horizontal frame member, thereby requiring both substantial strengthening of the horizontal member, as well as substantial strengthening of the vertical struts. The vertical struts had to be designed against cantilever forces, acting at a significant lever arm distance from the attachment point at the horizontal frame member.
Many of the drawbacks of the early prior trailers were overcome by aspects of U.S. Pat. Nos. 5,749,595, 5,551,759 and 5,549,359. The dual use vehicle or trailer described and claimed in those prior patents continued to require a significant amount of heavy structure to provide proper dual use capabilities. Because of certain physical and regulatory limitations for roads and bridges, the amount of weight of the trailer structure reduced the payload that could be carried.